U.S. patent application number 16/080692 was filed with the patent office on 2019-03-14 for module for gas separation, and gas separation method.
This patent application is currently assigned to Asahi Kasei Kabushiki Kaisha. The applicant listed for this patent is Asahi Kasei Kabushiki Kaisha. Invention is credited to Yasutaka KURISHITA, Masato MIKAWA, Azusa YAMANAKA.
Application Number | 20190076786 16/080692 |
Document ID | / |
Family ID | 59743087 |
Filed Date | 2019-03-14 |
![](/patent/app/20190076786/US20190076786A1-20190314-D00000.png)
![](/patent/app/20190076786/US20190076786A1-20190314-D00001.png)
![](/patent/app/20190076786/US20190076786A1-20190314-D00002.png)
![](/patent/app/20190076786/US20190076786A1-20190314-D00003.png)
United States Patent
Application |
20190076786 |
Kind Code |
A1 |
MIKAWA; Masato ; et
al. |
March 14, 2019 |
Module for Gas Separation, and Gas Separation Method
Abstract
Module for gas separation that maintains moisture retention of a
gas separation active layer at a uniform level has a composite
hollow-fiber membrane configured as the interior of an exterior
body and has a porous hollow-fiber support body and a gas
separation active layer disposed on the surface of the hollow-fiber
support body. The exterior body has a supply port and a discharge
port for a first gas passing through the outer side of the
composite hollow-fiber membrane, and a supply port and a discharge
port for a second gas passing through the inner side of the
composite hollow-fiber membrane. The first gas flows through a
first space enclosed by the exterior body and the outer side of the
composite hollow-fiber membrane and the second gas flows through a
second space separated by the composite hollow-fiber membrane and
the exterior body. The first space is filled with an absorbing
solution.
Inventors: |
MIKAWA; Masato; (Tokyo,
JP) ; KURISHITA; Yasutaka; (Tokyo, JP) ;
YAMANAKA; Azusa; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Asahi Kasei Kabushiki Kaisha |
Tokyo |
|
JP |
|
|
Assignee: |
Asahi Kasei Kabushiki
Kaisha
Tokyo
JP
|
Family ID: |
59743087 |
Appl. No.: |
16/080692 |
Filed: |
March 3, 2017 |
PCT Filed: |
March 3, 2017 |
PCT NO: |
PCT/JP2017/008580 |
371 Date: |
August 29, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 71/34 20130101;
B01D 63/00 20130101; B01D 53/228 20130101; B01D 61/00 20130101;
B01D 69/00 20130101; B01D 71/68 20130101; B01D 63/02 20130101; B01D
63/022 20130101; B01D 69/10 20130101; B01D 69/12 20130101 |
International
Class: |
B01D 63/02 20060101
B01D063/02; B01D 53/22 20060101 B01D053/22; B01D 69/10 20060101
B01D069/10; B01D 69/12 20060101 B01D069/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2016 |
JP |
2016-042529 |
Claims
1. A module for gas separation having a gas separation membrane
disposed in the interior of an exterior body, wherein the module
has a first space enclosed by the outer side of the gas separation
membrane and the exterior body and a second space on the inner side
of the gas separation membrane, the first space and second space
being separated by the gas separation membrane and exterior body,
and the first space is filled with an absorbing solution selected
from the group consisting of water, and liquids or ionic liquids
including at least one compound selected from the group consisting
of amines, amino acids, carbonates, silver salts and copper
salts.
2. The module for gas separation according to claim 1, wherein the
gas separation membrane is a hollow fiber membrane having a porous
hollow fiber support and a gas separation active layer situated on
the surface of the hollow fiber support.
3. The module for gas separation according to claim 1, wherein the
exterior body has a supply port and a discharge port for a first
gas that passes through the first space, and a supply port and a
discharge port for a second gas that passes through the second
space.
4. The module for gas separation according to claim 1, which has a
draft tube between the exterior body and the gas separation
membrane.
5. The module for gas separation according to claim 2, wherein the
hollow fiber membrane is a composite hollow fiber membrane having a
porous hollow fiber support and a gas separation active layer
situated on the surface of the hollow fiber support.
6. The module for gas separation according to claim 3, wherein the
first gas is a mixed gas including the gas component to be
separated, and the second gas is a feed gas that is to recover the
separated gas.
7. The module for gas separation according to claim 1, wherein
moisture is present in the second space.
8. The module for gas separation according to claim 7, wherein the
moisture content is 0.1% or higher and 5.0% or lower.
9. The module for gas separation according to claim 3, wherein the
discharge port and supply port for the first gas are connected.
10. The module for gas separation according to claim 9, wherein the
absorbing solution circulates through the discharge port and supply
port.
11. The module for gas separation according to claim 2, wherein the
gas separation active layer is composed mainly of a polymer gel,
and the thickness of the layer is 10 nm or greater and 10 .mu.m or
smaller.
12. The module for gas separation according to claim 11, wherein
the polymer gel is chitosan.
13. The module for gas separation according to claim 2, wherein the
porous hollow fiber support is composed mainly of polyethersulfone
or polyvinylidene fluoride.
14. The module for gas separation according to claim 2, which has
partitions that adhesively anchor both ends of the hollow fiber
membrane to the exterior body while separating the first space and
the second space, the partitions being made of an epoxy resin
obtained by curing a composition containing a compound with an
epoxy group as the base compound and a compound with an acid
anhydride group as a curing agent.
15. The module for gas separation according to claim 1, wherein the
first space is filled with an absorbing solution composed mainly of
an aqueous solution including at least one metal salt selected from
the group consisting of silver salts and copper salts, and the gas
separation layer also contains the same metal salt as the absorbing
solution.
16. The module for gas separation according to claim 1, wherein the
percentage of the first space occupied by the absorbing solution is
5 to 99 vol %.
17. The module for gas separation according to claim 15, wherein
the silver salt or copper salt in the absorbing solution filling
the first space is 5 wt % to 90 wt % with respect to the total
weight of the water.
18. The module for gas separation according to claim 1, wherein the
pressure conditions in the first space are 0.1 to 2.5 MPaG.
19. The module for gas separation according to claim 1, wherein the
moisture content of the second gas is 0.1 to 99%.
20. The module for gas separation according to claim 1, wherein the
content of inert gas in the second gas is 0.1 to 99%.
21. A gas separation method in which a module for gas separation
according to claim 1 is used to separate a gas to be separated from
a mixed gas, the method being carried out under conditions in which
the partial pressure of the gas to be separated in the first gas is
higher than the partial pressure of the gas to be separated in the
second gas.
22. A gas separation method in which moisture in a gas separated by
the gas separation method according to claim 21 is separated by
dehydrating equipment.
23. The gas separation method according to claim 21, wherein the
first gas is an olefin and/or carbon dioxide.
24. The gas separation method according to claim 23, wherein the
olefin contains any one of ethylene, propylene, isobutene, butene
or butadiene.
25. The gas separation method according to claim 23, wherein the
olefin is a bio-olefin.
26. The gas separation method according to claim 23, wherein the
olefin content of the gas after separation of moisture by the
dehydrating equipment is 99.99% or greater, and the paraffin
content is 0.1 to 100 ppm.
27. The gas separation method according to claim 21, which produces
olefin gas having a propane content of 0.1 to 50 ppm and a purity
of 99.995% or greater.
28. An olefin gas having a propane content of 0.1 to 50 ppm and a
purity of 99.995% or greater.
29. An olefin gas having an oxygen content of 0.1 to 5 ppm and a
purity of 99.995% or greater.
30. An olefin gas having a carbon dioxide content of 0.1 to 5 ppm
and a purity of 99.995% or greater.
31. The gas separation method according to claim 23, wherein the
olefin is produced from a fermentation gas.
Description
FIELD
[0001] The present invention relates to a module for gas separation
and a gas separation method whereby a desired gas component in a
source gas is absorbed into an absorbing solution and the desired
gas component in the absorbing solution is separated using a gas
separation membrane.
BACKGROUND
[0002] Separation and concentration of gases using gas separation
membranes is a method with more excellent energy efficiency and
higher safety compared to distillation or high-pressure adsorption
methods. Recently, methods using gas separation membranes to remove
and recover carbon dioxide, a greenhouse gas, from synthetic gas,
natural gas or the like are also being actively studied (see PTLs
1, 2 and 3, for example).
[0003] Gas separation membranes are commonly in a form having a
construction in which a gas separation active layer having gas
separative power is situated on the surface of a porous
support.
[0004] Such a form is effective for imparting a certain degree of
strength to the gas separation active layer while increasing the
amount of gas permeation. The separation layer in this case is
usually a layer containing a non-porous polymer.
[0005] The performance of a gas separation membrane is usually
represented by the indices of permeation rate and separation
factor. The permeation rate is represented as: (permeability
coefficient of gas)/(thickness of separation layer). As evident
from this formula, measures for obtaining a membrane with a high
permeation rate include reducing the thickness of the gas
separation active layer (see PTLs 4 and 5, for example), and
increasing the permeability coefficient of the gas. That is, in
order to obtain efficient membrane processing it is important to
use a material with a large permeability coefficient and separation
factor, and to reduce its thickness to a minimum. The separation
factor is a value represented by the ratio of the permeation rates
of the two gases that are to be separated, and this depends on the
gas separating polymer composing the gas separation membrane.
[0006] The structure of the gas separation membrane is usually an
asymmetric structure with a gas separation active layer having gas
separative power layered on a porous support. The porous support
has no ability to separate gases, but functions as a support to
bear the gas separation active layer which does have gas separative
power. The thickness of the gas separation active layer is on the
micron order. Further thickness reduction of the gas separation
active layer increases the productivity per module and is
significant from the viewpoint of rendering the separating
equipment more compact.
[0007] The olefin separating membrane is a membrane that separates
olefin components such as ethylene, propylene, 1-butene, 2-butene,
isobutene and butadiene from a mixed gas containing two or more gas
components. Such a mixed gas includes, in addition to olefins, also
mainly paraffins such as ethane, propane, butane and isobutane, and
carbon dioxide. Since olefins and paraffins in a mixed gas have
similar molecular sizes, the separation factor is generally small
in a dissolution and diffusion separation mechanism. However, it is
known that since olefins have affinity for silver ions and copper
ions, with which they form complexes, olefins can be separated from
mixed gases by an accelerated transport permeation mechanism
utilizing that complex formation.
[0008] An accelerated transport permeation mechanism is a
separation mechanism utilizing the affinity between a gas and a
membrane for the purpose of separation. The membrane itself may
have affinity, or the membrane may be doped with a component having
affinity.
[0009] It is common for an accelerated transport permeation
mechanism to yield a higher separation factor than a dissolution
and diffusion separation mechanism. In an accelerated transport
permeation mechanism for separation of an olefin, a metal ion is
necessary to produce affinity with the olefin, and therefore the
gas separation active layer must include water and an ionic liquid,
the gas separation active layer usually being in the form of a gel
membrane.
[0010] For carbon dioxide separating membranes as well, which
separate carbon dioxide from mixed gases, techniques are known for
separating carbon dioxide by an accelerated transport permeation
mechanism, similar to an olefin separating membrane. Carbon dioxide
generally has affinity for amino groups, and this separation
technique utilizes that affinity. Such a separating membrane also
usually includes water and an ionic liquid in the membrane, and the
gas separation active layer is usually in the form a gel
membrane.
[0011] In an accelerated transport permeation mechanism, when the
amount of moisture in the gas separation active layer decreases, it
becomes no longer possible to maintain affinity with the desired
gas components such as olefins or carbon dioxide, and the
permeability of the desired gas component is notably reduced. In a
gas separation apparatus, therefore, it is important to maintain a
state that includes moisture, in order to maintain the performance
of the gas separation active layer.
[0012] However, technology allowing moisture to be adequately
maintained has not yet been developed.
CITATION LIST
Patent Literature
[0013] [PTL 1] International Patent Publication No. WO2014/157069
[0014] [PTL 2] Japanese Unexamined Patent Publication No.
2011-161387 [0015] [PTL 3] Japanese Unexamined Patent Publication
HEI No. 9-898 [0016] [PTL 4] Japanese Patent Publication No.
5507079 [0017] [PTL 5] Japanese Patent Publication No. 5019502
SUMMARY
Technical Problem
[0018] As mentioned above, since the gas separation active layer in
an accelerated transport permeation mechanism usually requires
moisture, it is necessary to hold water in the gas separation
active layer using water vapor or the like in the source gas.
However, due to the extremely rapid permeation rate of water, there
is a limit to how uniformly water can be held in a gas separation
active layer in a gas separation apparatus. That is, because it is
difficult to maintain permeability in a membrane with low moisture,
there have been limitations to effective utilization of the
membrane area of gas separation active layers.
[0019] The present invention has been devised in light of these
circumstances of the prior art, and it is an object of the
invention to provide a module for gas separation that can uniformly
and continuously hold water in the gas separation active layer for
long periods.
Solution to Problem
[0020] The present inventors have conducted diligent research with
the goal of solving the problem described above. As a result it was
found that the problem can be solved by a module for gas separation
in which a composite hollow fiber membrane having a gas separation
active layer is disposed in the interior, the module being filled
with an absorbing solution for a gas component to be separated that
is present in a source gas, on the outer side of the composite
hollow fiber membrane, and containing moisture in a feed gas for
gas separation recovery, on the inner side of the composite hollow
fiber membrane, and the present invention has thereupon been
completed.
[0021] Specifically, the present invention provides the following.
[0022] [1]
[0023] A module for gas separation having a gas separation membrane
disposed in the interior of an exterior body, wherein the module
has a first space enclosed by the outer side of the gas separation
membrane and the exterior body and a second space on the inner side
of the gas separation membrane, the first space and second space
being separated by the gas separation membrane and exterior body,
and the first space is filled with an absorbing solution selected
from the group consisting of water, and liquids or ionic liquids
including at least one compound selected from the group consisting
of amines, amino acids, carbonates, silver salts and copper salts.
[0024] [2]
[0025] The module for gas separation according to [1], wherein the
gas separation membrane is a hollow fiber membrane having a porous
hollow fiber support and a gas separation active layer situated on
the surface of the hollow fiber support. [0026] [3]
[0027] The module for gas separation according to [1] or [2],
wherein the exterior body has a supply port and a discharge port
for a first gas that passes through the first space, and a supply
port and a discharge port for a second gas that passes through the
second space. [0028] [4]
[0029] The module for gas separation according to any one of [1] to
[3], which has a draft tube between the exterior body and the gas
separation membrane. [0030] [5]
[0031] The module for gas separation according to any one of [2] to
[4], wherein the hollow fiber membrane is a composite hollow fiber
membrane having a porous hollow fiber support and a gas separation
active layer situated on the surface of the hollow fiber support.
[0032] [6]
[0033] The module for gas separation according to any one of [1] to
[5], wherein the first gas is a mixed gas including the gas
component to be separated, and the second gas is a feed gas that is
to recover the separated gas. [0034] [7]
[0035] The module for gas separation according to any one of [1] to
[6], wherein moisture is present in the second space. [0036]
[8]
[0037] The module for gas separation according to [7], wherein the
moisture content is 0.1% or higher and 5.0% or lower. [0038]
[9]
[0039] The module for gas separation according to any of [3] to
[8], wherein the discharge port and supply port for the first gas
are connected. [0040] [10]
[0041] The module for gas separation according to [9], wherein the
absorbing solution circulates through the discharge port and supply
port. [0042] [11]
[0043] The module for gas separation according to any one of [2] to
[10], wherein the gas separation active layer is composed mainly of
a polymer gel, and the thickness of the layer is 10 nm or greater
and 10 .mu.m or smaller. [0044] [12]
[0045] The module for gas separation according to [11], wherein the
polymer gel is chitosan. [0046] [13]
[0047] The module for gas separation according to any one of [2] to
[12], wherein the porous hollow fiber support is composed mainly of
polyethersulfone or polyvinylidene fluoride. [0048] [14]
[0049] The module for gas separation according to any one of [2] to
[13], which has partitions that adhesively anchor both ends of the
hollow fiber membrane to the exterior body while separating the
first space and the second space, the partitions being made of an
epoxy resin obtained by curing a composition containing a compound
with an epoxy group as the base compound and a compound with an
acid anhydride group as a curing agent. [0050] [15]
[0051] The module for gas separation according to any one of [1] to
[14], wherein the first space is filled with an absorbing solution
composed mainly of an aqueous solution including at least one metal
salt selected from the group consisting of silver salts and copper
salts, and the gas separation layer also contains the same metal
salt as the absorbing solution. [0052] [16]
[0053] The module for gas separation according to any one of [1] to
[14], wherein the percentage of the first space occupied by the
absorbing solution is 5 to 99 vol %.
[0054] The module for gas separation according to any one of [1] to
[15], wherein the silver salt or copper salt in the absorbing
solution filling the first space is 5 wt % to 90 wt % with respect
to the total weight of the water. [0055] [18]
[0056] The module for gas separation according to any one of [1] to
[17], wherein the pressure conditions in the first space are 0.1 to
2.5 MPaG. [0057] [19]
[0058] The module for gas separation according to any one of [1] to
[18], wherein the moisture content of the second gas is 0.1 to 99%.
[0059] [20]
[0060] The module for gas separation according to any one of [1] to
[19], wherein the content of inert gas in the second gas is 0.1 to
99%. [0061] [21]
[0062] A gas separation method in which a module for gas separation
according to any one of [1] to [20] is used to separate a gas to be
separated from a mixed gas, the method being carried out under
conditions in which the partial pressure of the gas to be separated
in the first gas is higher than the partial pressure of the gas to
be separated in the second gas. [0063] [22]
[0064] A gas separation method in which moisture in a gas separated
by the gas separation method according to [21] is separated by
dehydrating equipment. [0065] [23]
[0066] The gas separation method according to [21] or [22], wherein
the first gas is an olefin and/or carbon dioxide. [0067] [24]
[0068] The gas separation method according to [23], wherein the
olefin contains any one of ethylene, propylene, isobutene, butene
or butadiene. [0069] [25]
[0070] The gas separation method according to [23], wherein the
olefin is a bio-olefin. [0071] [26]
[0072] The gas separation method according to [23] or [24], wherein
the olefin content of the gas after separation of moisture by the
dehydrating equipment is 99.99% or greater, and the paraffin
content is 0.1 to 100 ppm. [0073] [27]
[0074] The gas separation method according to any of [21] to [26],
which produces olefin gas having a propane content of 0.1 to 50 ppm
and a purity of 99.995% or greater. [0075] [28]
[0076] An olefin gas having a propane content of 0.1 to 50 ppm and
a purity of 99.995% or greater. [0077] [29]
[0078] An olefin gas having an oxygen content of 0.1 to 5 ppm and a
purity of 99.995% or greater. [0079] [30]
[0080] An olefin gas having a carbon dioxide content of 0.1 to 5
ppm and a purity of 99.995% or greater. [0081] [31]
[0082] The gas separation method according to any one of [23] to
[27], wherein the olefin is produced from a fermentation gas.
ADVANTAGEOUS EFFECTS OF INVENTION
[0083] According to the invention there is provided a module for
gas separation that has a high permeation rate and high separation
performance for gases to be separated, and that uniformly retains
moisture in the gas separation active layer continuously for long
periods, and as a result, can maintain high separation performance
for prolonged periods.
BRIEF DESCRIPTION OF DRAWINGS
[0084] FIG. 1 is a diagram showing the general construction of a
module for gas separation according to an embodiment of the
invention.
[0085] FIG. 2 is a diagram showing the general construction of a
module for gas separation according to an embodiment of the
invention.
[0086] FIG. 3 is a diagram showing the general construction of a
module for gas separation according to an embodiment of the
invention.
DESCRIPTION OF EMBODIMENTS
[0087] Embodiments of the invention will now be explained in
greater detail with reference to the accompanying drawings.
[Source Gas (First Gas)]
[0088] The source gas (first gas) of the invention is a mixed gas
of two or more gas components including the gas component to be
separated. The gas component to be separated is separated from the
mixed gas by being absorbed into an absorbing solution.
[0089] Examples for the gas component to be separated include
carbon dioxide, methane, ethane, ethylene, propane, propylene,
butane, and olefin gases such as 1-butene, 2-butene, isobutane,
isobutene and butadiene. An olefin gas is a hydrocarbon gas having
a double bond. An olefin gas may also be a bio-olefin gas
synthesized using mainly a polysaccharide as the starting material.
The olefin gas may also be produced from a fermentation gas.
[0090] The gas separation membrane of the invention may be a flat
membrane or a hollow fiber membrane.
[0091] The module for gas separation 1 of the invention preferably
comprises composite hollow fiber membranes 4, each having a porous
hollow fiber support 2 and a gas separation active layer 3 situated
on the surface of the porous hollow fiber support 2, disposed in
the interior of an exterior body 5.
[0092] As shown in FIG. 1, the module for gas separation 1
comprises a plurality of composite hollow fiber membranes 4, a
tubular exterior body 5 housing the composite hollow fiber
membranes 4 and partitions 6 (adhesive anchoring members) that
adhesively anchor both ends of each of the composite hollow fiber
membranes 4 to the exterior body 5. The partitions 6 define the
regions where the openings of the composite hollow fiber membranes
4 are exposed (second spaces) and the region enclosed by the outer
sides of the composite hollow fiber membranes 4 and the exterior
body 5 (first space).
[0093] In the tubular exterior body 5 there are provided a supply
port 5a that supplies a source gas (first gas) and a discharge port
5b that discharges treated gas, after the desired gas component has
been separated from the source gas, the supply port 5a and
discharge port 5b being provided in a manner protruding to the
outer side from the side surface of the exterior body 5. The source
gas (first gas) is supplied between the outer sides of the
composite hollow fiber membranes 4 and the exterior body 5 (first
space).
[0094] The partitions 6 and the header sections 7 are situated at
both ends of the exterior body 5, sealing the composite hollow
fiber membranes 4 inside the exterior body 5. At the header
sections 7 there are provided, respectively, a supply port 7a that
supplies a feed gas (second gas) for absorption of the separating
gas to the inner sides of the composite hollow fiber membranes 4,
and a discharge port 7b for discharge of the feed gas. The feed gas
(second gas) used is a different gas from the source gas (first
gas), and the feed gas (second gas) is supplied to the inner sides
of the composite hollow fiber membranes 4 (second spaces). A vacuum
pump may also be provided for transport of the absorbed gas
downstream from 7b.
[0095] As shown in FIG. 3, the module for gas separation 1 may have
draft tubes 12 situated between the exterior body 5 and the
composite hollow fiber membranes 4. The number of supply ports for
the first gas as the source gas may be one, but there is no
restriction on the number, with 4 or more being preferred however,
when draft tubes 12 are provided. When the source gas is fed to the
module for gas separation 1, the gas is blown in toward the draft
tubes 12 and moves to the liquid surface without contacting with
the composite hollow fiber membranes. Since a concentration
difference is produced on the outer sides and inner sides of the
draft tubes 12, liquid circulation is generated inside the module
for gas separation, and olefin gas absorbed into the liquid during
circulation is taken up into the composite hollow fiber membranes
4.
[0096] The draft tubes 12 used for the invention are tubes that
have been imparted with a function of agitating the absorbing
solution in the module for gas separation 1.
[0097] The draft tubes 12 are in partial anchored contact with the
exterior body or the partitions 6. Also, the bottom sides of the
draft tubes 12 are situated so as to be at a lower location than
the supply port 5a for the source gas. This will allow a density
difference to be efficiently created inside the absorbing solution,
without the source gas being directly taken up into the composite
hollow fiber membranes 4.
[0098] The top sides of the draft tubes 12 must also be lower than
the liquid surface of the absorbing solution. By configuring the
draft tubes 12 in this manner, it is possible to cause the
absorbing solution of the module for gas separation 1 to circulate
inside the module. The shapes of the draft tubes 12 may be circular
or polygonal. The shapes are not important so long as the structure
is such that it imparts a function of generating liquid circulation
inside the module.
[0099] The material for the draft tubes 12 is preferably a material
that is not degraded by the feed gas and the liquid in the inside
the module. Stainless steel, glass and zirconium are preferred. The
thickness of the draft tubes is preferably 10 .mu.m to 1 cm, with
50 .mu.m to 5 mm being more desirable.
[Porous Hollow Fiber Support]
[0100] The porous hollow fiber supports 2 for the gas separation
membrane of this embodiment are hollow fiber supports made of a
membrane having a plurality of fine pores running through and
connecting the front and back of each membrane. The porous hollow
fiber supports 2 exhibit essentially no gas separation performance,
but they can impart mechanical strength to the gas separation
membrane of this embodiment.
[0101] The material of which the porous hollow fiber supports 2 are
formed is not particularly restricted so long as it has sufficient
corrosion resistance against the source gas and absorbing solution
8 and sufficient durability at the operating temperature and
operating pressure, but preferred organic materials are
homopolymers or copolymers such as polyethersulfone, polyvinylidene
fluoride, PTFE, polyimide, polybenzooxazole and polybenzimidazole,
any one of which may be used alone or as mixtures.
[0102] The inner diameters of the porous hollow fiber supports 2
are appropriately selected depending on the throughput of the
source gas, but they will generally be selected between 0.1 mm and
20 mm. In order to increase contactability between the absorbing
solution 8 and the gas component to be separated which is present
in the source gas, the inner diameters of the porous hollow fiber
supports 2 are preferably 0.2 mm to 15 mm. The outer diameters of
the hollow fibers are not particularly restricted, and they may be
appropriately selected to have thickness that can withstand
differential pressure outside and inside the hollow fibers,
depending on the inner diameters of the porous hollow fiber
supports 2.
[Gas Separation Active Layer]
[0103] As mentioned above, the gas separation active layers 3 must
include a metal ion in order to produce affinity with the gas
component to be separated, and therefore the gas separation active
layers 3 are preferably in the form of gel membranes (polymer gel
membranes) containing water and an ionic liquid.
[0104] The thicknesses of the gas separation active layers 3 are
preferably small, and will generally be selected between 10 nm and
100 .mu.m. In order to increase the recovery speed of the desired
gas component that is present in the source gas, the thicknesses of
the gas separation active layers 3 are preferably 10 nm to 10
.mu.m.
[0105] The material of the gas separation active layers 3 may be,
for example, polyvinyl alcohol, polyacrylic acid,
poly(1-hydroxy-2-propyl acrylate), polyethylene oxide-modified
phosphoric acid methacrylate, polyallylsulfonic acid,
polyvinylsulfonic acid, polyacrylamidemethylpropanesulfonic acid,
polyethyleneimine, polyallylamine, gelatin, polylysine,
polyglutamic acid, polyarginine, polyglycidyl methacrylate,
poly(1-hydroxy-2-propyl acrylate) or polyethylene oxide-modified
phosphoric acid methacrylate.
[0106] The polymer gel membrane may also include a polysaccharide.
A polysaccharide, for the purpose of the present specification, is
a polymer having a structure in which a monosaccharide is bonded by
a glycoside bond, and the concept encompasses oligosaccharides. The
number of repeating units of the polysaccharide is preferably 100
to 10,000, more preferably 300 to 7,000 and even more preferably
500 to 4,000.
[0107] Examples of polysaccharides include chitosan, alginic acid,
pectin, chondroitin, hyaluronic acid, xanthan gum, cellulose,
chitin, pullulan, oligoglucosamine and oligofructose, as well as
their derivatives. These polysaccharides may be used alone or in
admixture.
[0108] The composite hollow fiber membranes 4 were described above,
but a specific metal salt may also be added to the porous hollow
fiber supports 2 and the gas separation active layers 3 that are
the main constituents of the composite hollow fiber membranes 4, in
order to improve the gas separation performance. From the viewpoint
of improving gas separation performance, the gas separation active
layers 3 preferably contain the same metal salt as the absorbing
solution.
[0109] The metal salt is preferably a salt consisting of a cation
selected from the group consisting of monovalent silver ions,
monovalent copper ions and their complex ions, and an anion
selected from the group consisting of F.sup.-, Cl.sup.-, Br.sup.-,
I.sup.-, CN.sup.-, NO.sub.3.sup.-, SCN.sup.-, ClO.sub.4.sup.-,
CF.sub.3SO.sub.3.sup.-, BF.sub.4.sup.- and PF.sub.6.sup.-, and
their mixtures. Of these, Ag(NO.sub.3) is especially preferred from
the viewpoint of ready availability and product cost.
[0110] The content of the metal salt is preferably 5 wt % to 90 wt
% and more preferably 10 wt % to 80 wt % with respect to the total
weight of the metal salt and water.
[Exterior Body]
[0111] The exterior body 5 in which the composite hollow fiber
membranes 4 are disposed will now be described.
[0112] The exterior body 5 may have any construction and shape so
long the composite hollow fiber membranes 4 can be disposed inside
it, but the example used here is of a cylindrical exterior body
5.
[0113] The cylindrical exterior body 5 is mainly constructed with a
cylindrical portion having a cylindrical shape open at one or both
ends for insertion of the composite hollow fiber membranes 4, and
partitions 6 and header sections 7 for sealing after insertion of
the composite hollow fiber membranes 4.
[Cylindrical Portion]
[0114] The cylindrical portion serves to internally house the
composite hollow fiber membranes 4 and isolate them from the
exterior, and the material of the cylindrical portion is not
particularly restricted so long as it has sufficient corrosion
resistance and durability against the source gas, absorbing
solution 8 and pressure, and may be a metal material, inorganic
material or organic material, or a composite material of the
same.
[0115] The cylindrical portion has at least a supply port 5a that
supplies the source gas (first gas) and a discharge port 5b that
discharges the treated gas after the desired gas has been separated
from the source gas. A plurality of supply ports 5a may also be
provided.
[Partitions]
[0116] The partitions 6 serve to expose the open ends of the
composite hollow fiber membranes 4 disposed inside the cylindrical
portion while sealing the composite hollow fiber membranes 4 in the
interior of the cylindrical portion, and such a construction
separates the inner sides of the composite hollow fiber membranes 4
from the outer sides of the composite hollow fiber membranes 4.
[0117] The partitions 6 of the module for gas separation 1 of this
embodiment are adhesive materials that join the composite hollow
fiber membranes 4 to the exterior body 5. The partitions 6 are
separating members serving to avoid mixing of the first gas and
second gas, while also being adhesive anchoring members that anchor
the composite hollow fiber membranes 4 to the exterior body 5.
[0118] The material of the partitions 6 is not particularly
restricted so long as it has sufficient corrosion resistance
against the source gas and absorbing solution and sufficient
durability against the operating temperature and operating
pressure, but usually an organic material such as a urethane resin,
epoxy resin, silicone resin, vinyl acetate resin or acrylic resin
may be used, with epoxy resins being preferred.
[0119] According to the invention, the partitions 6 must be durable
against the absorbing solution 8 since they will directly contact
with the absorbing solution 8. For this purpose, the members
forming the partitions 6 of the invention are durable against the
absorbing solution 8. The durability of epoxy resins is more
preferred.
[0120] The epoxy resin is obtained by mixing and curing a base
compound comprising a compound with an epoxy group, and a curing
agent. It may also include a curing accelerator.
[0121] Epoxy resin thermosetting agents include amines,
polyaminoamides, phenols and acid anhydrides, with acid anhydrides
being more preferred for use.
[0122] Examples of acid anhydrides include aliphatic acid
anhydrides such as methyl-5-norbornane-2,3-dicarboxylic anhydride
(methylnadic anhydride), dodecenylsuccinic anhydride, polyadipic
anhydride, polyazelaic anhydride, polysebacic anhydride,
poly(ethyloctadecanedioic acid) anhydride and
poly(phenylhexadecanedioic acid) anhydride, alicyclic acid
anhydrides such as methyltetrahydrophthalic anhydride,
methylhexahydrophthalic anhydride, methylhymic anhydride,
hexahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride
and methylcyclohexenedicarboxylic anhydride, or aromatic acid
anhydrides such as phthalic anhydride, trimellitic anhydride,
pyromellitic anhydride, benzophenonetetracarboxylic anhydride,
ethyleneglycol bis trimellitate and glycerol tris trimellitate, any
of which may be used alone or in admixture.
[0123] Common compounds such as tertiary amines including
tris(dimethylaminomethyl)phenol, 1,8-diazabicyclo[5,4,0]undecene-7
(DBU), 1,5-diazabicyclo[4.3.0]nonene-5 (DBN) and
1,4-diazabicyclo[2.2.2]octane (DABCO), imidazoles, Lewis acids and
Bronsted acids may be mentioned as epoxy resin curing accelerators,
any of which may be used alone or in admixture.
[0124] The epoxy-based adhesive may also include various additives
as necessary, such as fillers, age inhibitors and reinforcing
agents.
[Draft Tubes]
[0125] The draft tubes 12 are imparted with a function of agitating
the absorbing solution in the module for gas separation 1. By
creating a density difference of the liquid inside and outside of
the draft tubes 12, the absorbing solution is agitated and the
olefin gas is efficiently taken up into the composite hollow fiber
membranes 4.
[0126] The draft tubes 12 are in partial anchored contact with the
exterior body or the partitions 6. Also, the bottom sides of the
draft tubes 12 are situated at a lower location than the supply
port 5a for the source gas. This will allow a density difference to
be efficiently created inside the absorbing solution, without the
source gas being directly taken up into the composite hollow fiber
membranes 4.
[0127] The top sides of the draft tubes 12 must also be lower than
the liquid surface of the absorbing solution. By configuring the
draft tubes 12 in this manner, it is possible to cause the
absorbing solution of the module for gas separation 1 to circulate
inside the module. The shapes of the draft tubes may be circular or
polygonal. The shapes are not important so long as the structure is
one that imparts a function of generating liquid circulation inside
the module.
[0128] The material for the draft tubes is preferably a material
that is not degraded by the feed gas and the liquid in the inside
the module. Stainless steel, glass and zirconium are preferred.
[0129] The thickness of the draft tubes is preferably 10 .mu.m to 1
cm, with 50 .mu.m to 5 mm being more desirable.
(FIG. 3)
[0130] The module for gas separation 1 having the composite hollow
fiber membranes 4 disposed inside the exterior body 5 as described
above, due to its structure, allows supply of the source gas (first
gas) between the outer sides of the composite hollow fiber
membranes 4 and the exterior body 5 (first space) through the
supply port 5a, and discharge of the treated gas through the
discharge port 5b. It also has a structure that allows a feed gas
(second gas) for absorption of the separating gas, which is
different from the source gas (first gas), to be supplied to the
inner sides of the composite hollow fiber membranes 4 (second
spaces) through the supply port 7a, and discharged through the
discharge port 7b. The supply and discharge of the second gas may
be carried out through each of the composite hollow fiber membranes
4 one at a time, or through some of them at once, or through all of
the composite hollow fiber membranes at once, although it is more
efficient to carry it out through all of them at once (FIG. 1).
[Absorbing Solution]
[0131] The absorbing solution 8 is a liquid absorbent capable of
absorbing the gas component to be separated that is present in the
source gas, and it includes absorbents that cause absorption and
dissipation by reversible reaction with the gas component to be
separated, or that cause chemical or physical absorption and
dissipation. The absorbing solution 8 is selected from among known
chemical absorbing solutions, chemical absorbents, physical
absorbing solutions and physical absorbents.
[0132] The absorbing solution 8 is preferably filled in the space
through which the first gas passes (the first space), between the
composite hollow fiber membranes 4 and the exterior body 5 of the
module for gas separation 1. However, as shown in FIG. 1, the
absorbing solution 8 is filled without exceeding the height of the
discharge port 5b for the unabsorbed gas after treatment.
[0133] The filling volume of the absorbing solution 8 is 5 vol % to
99 vol %, preferably 20 vol % to 95 vol % and most preferably 25
vol % to 90 vol % of the first space.
[0134] In order to cause sufficient uptake of the gas component to
be separated into the absorbing solution, the volume percentage is
preferably 25 vol % or greater, and in order to efficiently
maintain the flow rate of the first gas, it is preferably no
greater than 90 vol %.
[0135] The type of absorbing solution 8 will differ depending on
the type of gas to be separated. For example, when the gas
component to be separated is carbon dioxide, examples of chemical
absorbing solutions (or absorbents) include amine absorbing
solutions of monoethanolamine, diethanolamine, triethanolamine,
diisopropylamine or methyldiethanolamine, amino acid aqueous
solutions of glycine or 2,3-diaminopropionic acid, carbonate
aqueous solutions or molten salts of potassium carbonate or the
like, and ionic liquids of imidazolium-based compounds or
pyridinium-based compounds.
[0136] When the desired gas component is an acidic gas such as
carbon dioxide, a physical absorbing solution (or adsorbent) may be
polyethylene glycol, dimethyl ether, methanol,
N-methyl-2-pyrrolidone, propylene carbonate, water or the like.
[0137] When the desired gas component is an olefin, examples of
absorbing solutions (or adsorbents) include metal salt aqueous
solutions, solutions of polyethylene glycol or the like, or cuprous
chloride aqueous solutions, and ionic liquids of imidazolium-based
compounds or pyridinium-based compounds, among which metal salts
are preferred.
[0138] The metal salt is preferably a salt consisting of a cation
selected from the group consisting of monovalent silver ions,
monovalent copper ions and their complex ions, and an anion
selected from the group consisting of F.sup.-, Cl.sup.-, Br.sup.-,
I.sup.-, CN.sup.-, NO.sub.3.sup.-, SCN.sup.-, ClO.sub.4.sup.-,
CF.sub.3SO.sub.3.sup.-, BF.sub.4.sup.- and PF.sub.6.sup.-, and
their mixtures. Of these, Ag(NO.sub.3) is especially preferred from
the viewpoint of ready availability and product cost.
[0139] The concentration of the metal salt in the absorbing
solution of the invention is preferably 10 mass % to 90 mass % ,
more preferably 30 mass % to 80 mass % and even more preferably 35
mass % to 75 mass % , with respect to the total mass of the water
and metal salt. When a silver salt or copper salt is used, it is
preferably 5 mass % to 90 mass % with respect to the total weight
of the water.
[0140] As mentioned above, these metal salts may be included in the
gas separation active layers 3, while also being included in the
porous hollow fiber supports 2.
[0141] Including such metal salts in both the absorbing solution 8
and composite hollow fiber membranes 4 will increase the gas
separation performance.
[Feed Gas for Absorption of the Separating Gas (Second Gas)]
[0142] The feed gas for absorption of the separating gas (second
gas), which is to recover the gas to be separated that has passed
through the composite hollow fiber membranes 4 and been separated
from the source gas (first gas), will now be described.
[0143] The second gas may be composed entirely of the separated
gas, but in order to sufficiently retain moisture in the gas
separation active layers 3 and maintain gas separation activity,
the second gas used is preferably a feed gas that is different from
the first gas that is to be separated.
[0144] The feed gas is preferably water vapor or an inert gas
including water vapor. The moisture content and inert gas content
of the second gas is preferably 0.1 to 99%, more preferably 10 to
99% and even more preferably 20 to 99%. The second gas itself may
also include moisture, or moisture may be present in the second
space. In this case, the moisture content in the second space is
0.1% or higher and 5.0% or lower.
[0145] Moisture is also separated from the separated gas if
necessary, using prescribed dehydrating equipment. Preferably, the
olefin content of the gas after separation of moisture by the
dehydrating equipment is 99.99% or greater and the paraffin content
is 0.1 to 100 ppm.
[Purified Gas]
[0146] Olefin gases such as propylene gas, as purified gases, can
reportedly be utilized as starting materials for synthesis of
acrylonitrile if their purity is 90 to 99%, and can reportedly be
utilized as starting materials for synthesis of polypropylene if
their purity is 99.5% or higher. Propylene with a high purity of
about 99.99% can reportedly be utilized as a carbon source for an
amorphous carbon layer, for manufacture of semiconductor memory.
However, high-purity propylene that is actually used at the current
time does not give a sufficient yield of amorphous carbon layer for
memory manufacturing.
[0147] The present inventors therefore conducted research to
discover the reason why a sufficient amorphous carbon layer yield
is not obtained despite high purity, focusing on the concentration
of propane, oxygen and carbon dioxide in high-purity propylene. As
a result of this research, it was found that the amorphous carbon
layer yield increases if the propane content in high-purity
propylene can be controlled to 1 ppm to 50 ppm and the oxygen
concentration and carbon dioxide concentration can be controlled to
0.1 ppm to 5 ppm.
[0148] When the propane concentration in high-purity propylene is
50 ppm or lower, the amorphous carbon layer yield tends to
increase, while conversely if the propane content is lower than 1
ppm the amorphous carbon layer strength tends to vary, requiring
more time for etching of the amorphous carbon layer, and therefore
a propane content of 0.1 ppm or greater may be considered optimal
for the etching step.
[0149] The same trend was found for oxygen and carbon dioxide as
well. When the oxygen or carbon dioxide concentration in
high-purity propylene is 5 ppm or lower, the amorphous carbon layer
yield tends to increase, while conversely if the oxygen or carbon
dioxide content is lower than 0.1 ppm the amorphous carbon layer
strength tends to vary, requiring more time for etching of the
amorphous carbon layer, and therefore an oxygen or carbon dioxide
content of 0.1 ppm or greater may be considered optimal for the
etching step.
[0150] In other words, the concentration of propane as the carbon
source of an amorphous carbon layer for semiconductor memory
manufacturing is preferably 0.1 ppm or greater as the lower limit
and no greater than 50 ppm as the upper limit. Moreover, the oxygen
concentration and carbon dioxide concentration during production of
an amorphous carbon layer for semiconductor memory manufacturing
are preferably 0.1 ppm or greater as the lower limit and no greater
than 5 ppm as the upper limit. Also, the propylene concentration is
preferably 99.995% or greater as the lower limit and no greater
than 99.9999% as the upper limit.
[0151] The module for gas separation 1 of the invention may have a
permeability coefficient of 100 Barrer or greater and 2,000 Barrer
or smaller for propylene gas and a propylene/propane separation
factor a of 50 or greater and 2,000 or smaller, under conditions
with a measuring temperature of 30.degree. C. and a propylene
partial pressure of 0.6 atmosphere.
[0152] The pressure of the source gas fed to the gas separation
module (the pressurization conditions in the first space) is
preferably 0.1 to 2.5 MPaG, more preferably 0.1 to 2.0 MPaG and
even more preferably 0.1 to 1.5 MPaG. At 0.1 MPaG or lower the
permeation rate of the olefin gas that is recovered will not be
sufficient, and at 2.5 MPaG or higher it will not be possible to
maintain the durability of the gas separation membrane.
[Mechanism of Olefin Gas Separation by Module for Gas Separation
1]
[0153] The mechanism by which gas separation is efficiently carried
out by the invention will now be explained.
[0154] In the module for gas separation 1 illustrated in FIG. 1,
the source gas (first gas) supplied from the supply port 5a for the
source gas contacts with the absorbing solution 8 that has been
supplied between the inner surface of the exterior body 5 and the
outer surfaces of the composite hollow fiber membranes 4 (first
space). Mass transfer of the gas component to be separated is
promoted, resulting in dissolution in the absorbing solution 8 in a
short period of time. This is because the metal salt in the
absorbing solution 8 is in ion form in the presence of water, and
it rapidly forms a complex with the olefin in the source gas.
[0155] Although the membrane permeation rate of water molecules is
extremely high, the gas separation active layers 3 do not dry
because the interior of the module for gas separation 1 is filled
with water (absorbing solution 8). In other words, the conventional
behavior in which the membranes dry, significantly lowering the
permeation rate, is not observed with the present invention.
[0156] The gas component to be separated that has dissolved in the
absorbing solution 8 increases in concentration in the absorbing
solution 8. The partial pressure ratio of the olefin and other
gases in the absorbing solution (olefin/other gases) is increased
above that in the source gas. Moreover, since the olefin gas that
has dissolved in the absorbing solution experiences accelerated
mass transfer into the composite hollow fiber membranes 4, which
have low olefin concentration, the desired component is separated
through an absorbed gas discharge line (not shown) connected to the
discharge port 7b. This is carried out with a higher partial
pressure of the gas to be separated in the first gas than the
partial pressure of the gas to be separated in the second gas.
[0157] The gas discharged from the absorbed gas discharge line
(discharge port 7b) may also include an inert gas or water vapor.
If it includes an inert gas, the difference between the gas partial
pressure of the gas component to be separated inside the absorbing
solution 8 and the partial pressure of the gas component to be
separated in the absorbed gas line can be increased, allowing a
high permeation rate to be continuously maintained. When an inert
gas is used, however, a subsequent step is necessary to separate
the olefin gas and the inert gas. For example, the gases can be
easily separated by cooling to a temperature at which the olefin
gas liquefies.
[0158] Supplying moisture into the absorbed gas line has the effect
of retaining moisture inside the composite hollow fiber membranes
4, and is effective as a method of preventing reduction in the
permeation rate due to lack of moisture retention. A subsequent
separation step is necessary for this moisture as well. It can be
easily separated using an absorptive material such as zeolite, for
example. The source gas that has not been absorbed into the
absorbing solution 8 is discharged from the module for gas
separation 1 through the discharge port 5b as unabsorbed gas. The
unabsorbed gas includes the unabsorbed portion of the desired
component present in the source gas, as well as gas components
other than the desired gas component.
[0159] Also, as shown in FIG. 2, in the module for gas separation
of the invention, the discharge port 5b for the first gas is
connected to the supply port 5a for the first gas via a circulation
line 9 and a gas absorption tube 10. In addition, a circulating
pump 11 situated within the circulation line 9 may be used to
circulate the absorbing solution 8. This is effective as a method
of reducing concentration polarization of gas in the absorbing
solution 8, and allows the desired gas component to be recovered at
a higher speed than the process of FIG. 1.
[0160] Furthermore, if draft tubes 12 are situated inside the
module for gas separation 1 as shown in FIG. 3, then the agitating
effect using the density difference inside the module can be
increased, and as a result, it is possible to efficiently take up
the olefin gas into the composite hollow fiber membranes 4.
[0161] As explained above, according to the present invention it is
possible to provide a module for gas separation and a gas
separation method that allow moisture to be continuously retained
for long periods in gas separation active layers, and to thereby
maintain high separation performance for prolonged periods.
EXAMPLES
[0162] The present invention will now be explained in further
detail using working examples. However, it is to be understood that
the invention is not limited in any way by these examples.
Example 1
[0163] A module for gas separation such as shown in FIG. 1 was
fabricated.
[0164] For the hollow fiber supports, polyethersulfone (PES) hollow
fiber membranes each having an inner diameter of 0.7 mm, an outer
diameter of 1.2 mm and a length of 12 cm were immersed in a 0.5 wt
% aqueous solution of chitosan and dried at 80.degree. C. for 7
minutes after immersion, to coat the hollow fiber support surfaces
with a chitosan layer as a gas separation active layer. Composite
hollow fiber membranes were fabricated in this manner.
[0165] Ten of the composite hollow fiber membranes were placed in a
cylindrical container having an inner diameter of 2 cm, and both
ends of the container were adhesively sealed with an acid
anhydride-based epoxy adhesive. The membrane area was 64 cm.sup.2.
After curing of the adhesive, 1 cm was cut from both ends of the
cylinder. A 7 M silver nitrate aqueous solution was injected into
the module for gas separation through a source gas supply line
(supply port 5a) on the side of the cylindrical container, to
fabricate a module for gas separation.
[0166] The module for gas separation was used for measurement of
the permeation rates for propane and propylene.
[0167] A mixed gas comprising propane and propylene as the first
gas (source gas) (propane:propylene=40:60 (mass ratio)) was used
for the measurement, with a supply side gas flow rate of 50 cc/min
and a nitrogen flow rate of 50 cc/min into the absorbed gas. The
nitrogen gas as the second gas (feed gas) was supplied into the
module for gas separation in a humidified atmosphere that had been
bubbled through water before being supplied. The measuring
temperature was 30.degree. C. The pressure was 0 KPaG for both the
first gas and second gas.
[0168] The gas component that permeated the module for gas
separation was analyzed by gas chromatography (GC) 3 hours after
supply of the source gas, and the propylene/propane separation
factor .alpha. was determined.
[0169] The measurement results are shown in Table 1.
Example 2
[0170] Measurement of gas permeation was carried out by the same
method as Example 1, except that instead of the humidified nitrogen
gas in Example 1, dry nitrogen gas that had not been bubbled in
water was used as the second gas.
[0171] The results are shown in Table 1.
Example 3
[0172] In Example 1, the unabsorbed gas line (discharge port 5b)
and source gas line (supply port 5a) were connected via a
circulating pump 11 and gas absorption tube 10 comprising a gas
supply line 10a and a gas discharge line 10b. The process is shown
in FIG. 2.
[0173] In FIG. 2, the source gas is supplied by a gas supply line
10a at the bottom end of the gas absorption tube 10, and the
unabsorbed gas is discharged through the gas discharge line 10b at
the top end of the gas absorption tube 10. The gas-dissolving
absorbing solution 8 was ejected from the bottom of the gas
absorption tube 10, and the solution alone was supplied to the
module for gas separation 1 by the circulating pump 11. The supply
solution is supplied into the module form the bottom of the module
for gas separation 1 and extracted from the top, and then supplied
to the top of the gas absorption tube 10.
[0174] The circulation rate of the absorbing solution was 30
cc/min.
[0175] The permeated gas component was analyzed by gas
chromatography (GC) 3 hours after circulation of the absorbing
solution.
[0176] The results are shown in Table 1.
Example 4
[0177] The permeation was measured by the same method as Example 3,
except that the circulation time for the absorbing solution was 7
days.
[0178] The results are shown in Table 1.
Example 5
[0179] The permeation was measured by the same method as Example 3,
except that a urethane adhesive was used instead of the acid
anhydride-based epoxy adhesive.
[0180] The results are shown in Table 1.
Example 6
[0181] The permeation was measured by the same method as Example 4,
except that a urethane adhesive was used instead of the acid
anhydride-based epoxy adhesive.
[0182] The results are shown in Table 1.
Example 7
[0183] The permeation was measured by the same method as Example 3,
except that the hollow fiber supports were polyvinylidene fluoride
(PVDF) instead of PES.
[0184] The results are shown in Table 1.
Example 8
[0185] The permeation was measured by the same method as Example 4,
except that the hollow fiber supports were PVDF instead of PES.
[0186] The results are shown in Table 1.
Example 9
[0187] The permeation was measured by the same method as Example 3,
except that the hollow fiber supports were polysulfone (PSf)
instead of PES.
[0188] The results are shown in Table 1.
Example 10
[0189] The permeation was measured by the same method as Example 4,
except that the hollow fiber supports were PSf instead of PES.
[0190] The results are shown in Table 1.
Example 11
[0191] The permeation was measured by the same method as Example 1,
except that the hollow fiber supports were polyvinylidene fluoride
(PVDF) instead of PES.
[0192] The results are shown in Table 1.
Example 12
[0193] The permeation was measured by the same method as Example
11, except that the measuring time was 7 days.
[0194] The results are shown in Table 1.
Example 13
[0195] The permeation was measured by the same method as Example 1,
except that the support was PVDF, a mixed gas comprising propane
and propylene (propane:propylene:oxygen:carbon
dioxide=0.49:99.5:0.005:0.005 (mass ratio)) was used as the first
gas (source gas), the supply side gas flow rate was 50 cc/min and
the nitrogen flow rate into the absorbed gas was 50 cc/min. The
results are shown in Table 1.
Example 14
[0196] The permeation was measured by the same method as Example
13, except that the measuring time was 7 days.
[0197] The results are shown in Table 1.
Example 15
[0198] A module for gas separation such as shown in FIG. 3 was
fabricated.
[0199] For the hollow fiber supports, polyvinylidene fluoride
(PVDF) hollow fiber membranes each having an inner diameter of 0.7
mm, an outer diameter of 1.2 mm and a length of 12 cm were immersed
in a 0.5 wt % aqueous solution of chitosan and dried at 80.degree.
C. for 7 minutes after immersion, to coat the hollow fiber support
surfaces with a chitosan layer as a gas separation active layer.
Composite hollow fiber membranes were fabricated in this
manner.
[0200] Thirty of the composite hollow fiber membranes were placed
in a cylindrical container having an inner diameter of 3 cm, and
both ends of the container were adhesively sealed with an acid
anhydride-based epoxy adhesive. The membrane area was 192 cm.sup.2.
After curing the adhesive, the acid anhydride epoxy adhesive bonded
to the hollow fibers was detached from the cylindrical container.
It was then inserted into a container in which draft tubes 12 with
inner diameters of 4 cm and an exterior body 5 with an inner
diameter of 5.5 cm were partially connected, both ends were cured
with an epoxy adhesive, and 1 cm was cut from both end surfaces.
The exterior body 5 used had four source gas supply ports 5a. A 7 M
silver nitrate aqueous solution was injected into the module to
obtain a module for gas separation 1.
[0201] The module for gas separation was used for measurement of
the permeation rates for propane and propylene.
[0202] A mixed gas comprising propane and propylene as the first
gas (source gas) (propane:propylene:oxygen:carbon
dioxide=0.49:99.5:0.005:0.005 (mass ratio)) was used for the
measurement, with a supply side gas flow rate of 150 cc/min and a
nitrogen flow rate of 200 cc/min into the absorbed gas. The
nitrogen gas as the second gas (feed gas) was supplied into the
module for gas separation in a humidified atmosphere that had been
bubbled through water before being supplied. The measuring
temperature was 30.degree. C. The pressure was 0 KPaG for both the
first gas and second gas.
[0203] The gas component that permeated the module for gas
separation was analyzed by FID gas chromatography (FID-GC) 3 hours
after supply of the source gas, and the propylene/propane
separation factor a was determined.
[0204] The measurement results are shown in Table 1.
Example 16
[0205] The permeation was measured by the same method as Example
15, except that the measuring time was 7 days.
[0206] The results are shown in Table 1.
Example 17
[0207] The permeation was measured by the same method as Example
15, except that a mixed gas comprising carbon dioxide and butadiene
(carbon dioxide:butadiene=65:35 (mass ratio)) was used as the first
gas (source gas).
[0208] The results are shown in Table 1. The Flux values in the
table indicate the butadiene permeation flow rates.
Example 18
[0209] The permeation was measured by the same method as Example
17, except that the measuring time was 7 days.
Example 19
[0210] The permeation was measured by the same method as Example
15, except that a mixed gas comprising carbon dioxide and butadiene
(carbon dioxide:nitrogen=30:70 (mass ratio)) was used as the first
gas (source gas), and the absorbing solution inside the module for
gas separation 1 was monoethanolamine.
[0211] The results are shown in Table 1. The Flux values in the
table indicate the carbon dioxide permeation flow rates.
Example 20
[0212] The permeation was measured by the same method as Example
19, except that the measuring time was 7 days.
Comparative Example 1
[0213] The permeation was measured by the same method as Example 2,
except that the absorbing solution was held in the module for gas
separation for 24 hours after being injected, after which the
absorbing solution was discharged from the unabsorbed gas line
(discharge port 5b) shown in FIG. 1.
[0214] The results are shown in Table 1.
Comparative Example 2
[0215] In Comparative Example 1, the source gas was supplied to the
module for gas separation after having been bubbled in water. The
permeation was measured by the same method, except that the
nitrogen in the absorbed gas line was also supplied to the module
for gas separation after having been bubbled in water.
[0216] The results are shown in Table 1.
Comparative Example 3
[0217] The permeation was measured by the same method as
Comparative Example 2, except that the measuring time was 7
days.
Comparative Example 4
[0218] The permeation was measured by the same method as Example 1,
except that the module for gas separation was assembled without
coating the hollow fiber supports with chitosan.
[0219] The results are shown in Table 1.
Comparative Example 5
[0220] The permeation was measured by the same method as
Comparative Example 1, except that the silver nitrate aqueous
solution was not used.
[0221] The results are shown in Table 1.
Comparative Example 6
[0222] In Comparative Example 5, purified water was injected into
the module for gas separation 1, and the source gas was supplied to
the module for gas separation. The permeation was measured by the
same method, except that the nitrogen in the absorbed gas line was
supplied to the module for gas separation after having been bubbled
in water.
[0223] The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Membrane Absorbing area solution in Liquid
Measurement or First gas (source gas) Support Adhesive [cm.sup.2]
module circulation circulation time Type Example 1 PES Epoxy 64 Yes
No 3 hours Propane:propylene = Example 2 PES Epoxy 64 Yes No 3
hours 40:60 Example 3 PES Epoxy 64 Yes Yes 3 hours Example 4 PES
Epoxy 64 Yes Yes 7 days Example 5 PES Urethane 64 Yes Yes 3 hours
Example 6 PES Urethane 64 Yes Yes 7 days Example 7 PVDF Epoxy 64
Yes Yes 3 hours Example 8 PVDF Epoxy 64 Yes Yes 7 days Example 9
PSf Epoxy 64 Yes Yes 3 hours Example 10 PSf Epoxy 64 Yes Yes 7 days
Example 11 PVDF Epoxy 64 Yes No 3 hours Example 12 PVDF Epoxy 64
Yes No 7 days Example 13 PVDF Epoxy 64 Yes No 3 hours
Propane:propylene:O.sub.2:CO.sub.2 = Example 14 PVDF Epoxy 64 Yes
No 7 days 0.49:99.5:0.005:0.005 Example 15 PVDF Epoxy 192 Yes No 3
hours Example 16 PVDF Epoxy 192 Yes No 7 days Example 17 PVDF Epoxy
192 Yes No 3 hours CO.sub.2:butadiene = Example 18 PVDF Epoxy 192
Yes No 7 days 65:35 Example 19 PVDF Epoxy 192 Yes No 3 hours
CO.sub.2:N.sub.2 = 30:70 Example 20 PVDF Epoxy 192 Yes No 7 days
Comp. Ex. 1 PES Epoxy 64 No No 3 hours Propane:propylene = Comp.
Ex. 2 PES Epoxy 64 No No 3 hours 40:60 Comp. Ex. 3 PES Epoxy 64 No
No 7 days Comp. Ex. 4 PES Epoxy 64 Yes No 3 hours Comp. Ex. 5 PES
Epoxy 64 No No 3 hours Comp. Ex. 6 PES Epoxy 64 Yes No 3 hours
First gas (source gas) Second gas (Feed gas) Flow rate Flow rate
Flux [cc/min] Humidification Type [cc/min] Humidification [cc/min]
A Example 1 50 No N.sub.2 50 Yes 6.8 >300 Example 2 50 No 50 No
6.0 >300 Example 3 50 No 50 Yes 7.8 >300 Example 4 50 No 50
Yes 7.8 >300 Example 5 50 No 50 Yes 7.4 >300 Example 6 50 No
50 Yes 7.8 162 Example 7 50 No 50 Yes 7.8 >300 Example 8 50 No
50 Yes 7.8 >300 Example 9 50 No 50 Yes 7.8 >300 Example 10 50
No 50 Yes 2.1 >300 Example 11 50 No 50 Yes 6.5 >300 Example
12 50 No 50 Yes 6.5 >300 Example 13 50 No 50 Yes 12.8 512
Example 14 50 No 50 Yes 12.9 509 Example 15 150 No 150 Yes 41 512
Example 16 150 No 150 Yes 40.5 509 Example 17 150 No 150 Yes 12.5
64 Example 18 150 No 150 Yes 13.2 62 Example 19 150 No 150 Yes 12
75 Example 20 150 No 150 Yes 11.9 80 Comp. Ex. 1 50 No 50 No Nd Nd
Comp. Ex. 2 50 Yes 50 Yes 5.1 >300 Comp. Ex. 3 50 Yes 50 Yes 4.5
>300 Comp. Ex. 4 50 No 50 Yes 7.9 23 Comp. Ex. 5 50 No 50 No Nd
Nd Comp. Ex. 6 50 No 50 Yes <0.1 Nd
[0224] As clearly seen in Table 1, gas permeation could not be
detected in Comparative Example 1, in which the first gas and
second gas had not been humidified. In Comparative Example 3, where
operation was carried out for 7 days according to Comparative
Example 2 in which the module interior was not filled with an
absorbing solution, a low separation factor a was obtained.
[0225] A low separation factor a was also obtained in Comparative
Example 4, in which no chitosan layer was coated.
[0226] In both Comparative Examples 5 and 6, in which the module
for gas separation 1 did not contain a metal salt, the propylene
gas permeability was low and the separation factor a was low,
regardless of the presence of a humidified atmosphere.
[0227] In contrast, in Examples 1 and 2 in which the module was
filled with an absorbing solution, a high separation factor a of
higher than 300, for example, was obtained. Moreover, by
circulating the absorbing solution as in Example 3, it was possible
to lower the concentration polarization of gas in the absorbing
solution and recover the desired gas component at a high speed.
However, while a lowered separation factor was observed during a
prolonged period of 7 days in Examples 5 and 6 in which the
adhesive was urethane, a high separation factor a was maintained
even for a prolonged period of 7 days in Example 4 where the
adhesive was an epoxy adhesive.
[0228] Furthermore, when the supports of the composite hollow fiber
membranes were changed to PSf from PES, as in Examples 9 and 10, a
lowering of the separation factor was observed during a prolonged
period of 7 days. When the supports of the composite hollow fiber
membranes were changed to PVDF from PES, as in Examples 7, 8, 11
and 12, there was no lowering of the separation factor during a
prolonged period of 7 days, and satisfactory results were
obtained.
[0229] When the source gas was 99.5% propylene gas, as in Examples
13 and 14, the propylene partial pressure of the first gas was
higher compared to Examples 1 to 10, and therefore the Flux
increased and the separation factor .alpha. was >500. The
propane concentration of the permeation gas was 0.1 to 50 ppm, with
100 as the total amount of propylene, propane, oxygen and carbon
dioxide. The propylene concentration was 99.995% or greater, the
oxygen concentration was 0.1 to 5 ppm and the carbon dioxide
concentration was 0.1 to 5 ppm.
[0230] When draft tubes were used as in Examples 15 and 16, the
absorbing solution circulation speed inside the module for gas
separation 1 was higher than in Examples 13 and 14, and therefore
the Flux further increased. The separation factor a was >500,
which was equal to Examples 13 to 14.
[0231] Even when a mixed gas of butadiene and carbon dioxide was
used for the first gas as in Examples 17 and 18, it was possible to
separate the butadiene as olefin gas.
[0232] When a mixed gas of carbon dioxide and nitrogen was used as
the first gas as in Examples 19 and 20, carbon dioxide could be
separated by using an amine-based absorbing solution, for
example.
[0233] The embodiments of the invention described above are not
intended to place limitations on the invention, and various
modifications may be incorporated such as fall within the gist of
the invention.
INDUSTRIAL APPLICABILITY
[0234] By using a module for gas separation according to the
present invention it is possible to obtain a high permeation rate
and high separation performance for desired gases, to continuously
retain water in the gas separation active layer uniformly for
prolonged periods and therefore to maintain high separation
performance for prolonged periods, and it can be widely used as a
module for gas separation that separates and recovers olefin gases
or carbon dioxide from synthetic gas or natural gas, as for
example, a module for gas separation that produces hydrocarbon gas
as an amorphous carbon source for a semiconductor process, or a
module for gas separation that separates and recovers bio-olefin
gas synthesized using mainly polysaccharides as starting
material.
REFERENCE SIGNS LIST
[0235] 1 Module for gas separation [0236] 2 Hollow fiber support
[0237] 3 Gas separation active layer [0238] 4 Composite hollow
fiber membrane [0239] 5 Exterior body [0240] 5a Source gas (first
gas) supply port [0241] 5b Source gas (first gas) discharge port
[0242] 6 Partition [0243] 7 Header section [0244] 7a Feed gas
(second gas) supply port [0245] 7b Feed gas (second gas) discharge
port [0246] 8 Absorbing solution [0247] 9 Circulation line [0248]
10 Gas absorption tube [0249] 10a Source gas supply line [0250] 10b
Unabsorbed gas discharge line [0251] 11 Circulating pump [0252] 12
Draft tube
* * * * *